1. Field of the Invention
This invention relates to method and apparatus for printing images, and more particularly to method and apparatus for printing images wherein the level of ink surface is risen by means of Coulomb force, whereby the ink is allowed to transfer onto printing paper to print the images.
2. Description of the Prior Art
An ink jet printing method has heretofore been known as a printing method of type wherein ink is caused to transfer onto printing paper thereby printing images. In such ink jet printing method, printing of images is effected by controlling ink drops jetted from an ink nozzle. This method has widely been used because images can be printed on ordinary papers. The ink jet printing method is constructed such that principal scanning is carried out by either deflecting ink drops or moving the nozzle. However, in such a case where 1 m/sec or more high-speed scanning is performed as required in facsimiles, plotters or the like, it is difficult in general to scan ink jet at such a high speed. For this reason, such a method has been adopted in which principal scanning is performed by means of cylindrical scanning and auxiliary scanning is performed by moving the nozzle when high speed scanning is required. However, the method utilizing the cylindrical scanning has defects in mounting and removal of printing papers, operation reliability, etc. so that such problems as described above remain unsolved when image printing with high pecision is required.
In this connection, Japanese Patent Laid-open Nos. 161933/1979 and 4467/1981 disclose an image printing apparatus employing a slit-jet method wherein ink is transferred directly onto ordinary papers by means of flat scanning thereby to reproduce images on the papers. This type of apparatus is constructed such that an ink nozzle whose opening is slit shaped is provided along the whole width in its scanning direction, a plurality of electrodes are juxtaposed inside the nozzle thereby forming a printing head, and ink jetted from the ink nozzle is controlled by selectively applying voltage to these electrodes. In forming such printing head, nozzle opening should be formed into a slit-shape and in addition, a plurality of electrodes should be disposed in the vicinity of the nozzle opening. In fabricating these electrodes, either a PWB (Printing Wiring Board) process utilizing etching technique or a process wherein a thin metal wires are uniformly juxtaposed to the portions where the electrodes are to be formed is used.
In the PWB process, however, it is difficult to form wide electrodes along the principal scanning direction, besides the electrodes formed by photoetching corroded easily. Further, it is difficult to uniformly dispose metal wires with an equal distance when the latter process is employed so that it has been a cause for deterioration of printing quality. In addition, since a plurality of electrodes are juxtaposed to each other with a small distance in the slit-jet method, there have been such problems that if conductive foreign substances are included in ink, there is a fear of short-circuiting of the electrodes, and further that if the ink existing between electrodes hardens, such hardened ink is difficult to remove.